The present invention relates to a remote copy system and a remote copy control method and, for instance, can be suitably applied to a storage system comprising a snapshot function.
Conventionally, snapshot has been used as one type of technology that is handled in a network storage such as a NAS (Network Attached Storage). Snapshot is technology of logically retaining a static data image of a primary volume (logical volume storing user data) at the point in time that a snapshot creation command was received. This snapshot is used when restoring a data image of the primary volume at the point in time that the snapshot was created when data of the primary volume is lost due to a man-caused error.
In addition, a remote copy system is known where, upon updating data of the primary volume, pre-update data is saved as differential data in a differential volume, and differential data saved in the differential volume is remote-copied to a storage apparatus installed in a secondary site. According to this remote copy system, even if the primary site including the primary volume is subject to a disaster, the data image of the primary volume can be restored by using the differential data that is retained in the storage apparatus of the secondary site.
As an example using the foregoing types of technologies, for instance, proposed is a snapshot management method which attempts to improve the user-friendliness of the user by periodically acquiring snapshots, detecting the degree of difference between two acquired snapshots, and, if the detected degree of difference is smaller than a predetermined threshold, deleting the snapshot that was acquired first of the two snapshots (refer to Japanese Patent Laid-Open Publication No. 2007-219609).
Moreover, proposed is a NAS system for appropriately remote-copying differential data of a snapshot based on a pre-scheduled remote copy start time by adjusting the Nth snapshot acquisition time or the Nth or (N+1)th remote copy start time so that the Nth remote copy ends before the (N+1)th remote copy start time (refer to Japanese Patent Laid-Open Publication No. 2007-193451).